Attenuating power supply output volts

[garry parker]

I need to build a power supply for a tube amp.
My transformer has an output of 240 volts, but after rectification this
rises to 330 volts.
I need a supply ouput of 250v dc.
Is there any way that I can reduce the 330 volts to 250 volts?
The transformer is rated at 100ma, and the amp will be drawing about 65ma.
The supply doesn't need to be regulated.

Thanks a lot.
Garry

 

[Rheilly Phoull]

"garry parker" <nospam@nospam.com> wrote in message
news:bt2ar0$dvh$1@newsg1.svr.pol.co.uk...

I need to build a power supply for a tube amp.
My transformer has an output of 240 volts, but after rectification this
rises to 330 volts.
I need a supply ouput of 250v dc.
Is there any way that I can reduce the 330 volts to 250 volts?
The transformer is rated at 100ma, and the amp will be drawing about 65ma.
The supply doesn't need to be regulated.

Thanks a lot.
Garry



The old way was to use a choke (inductor) in series, which with the addition

of the usual smoothing caps gave a nice clean DC. Of later years the trend
is towards a resistor, the snag for you might be the power dissipation. At
65mA it would be a tad over 5w so you would need a 10 watt resistor around
the 1000 ohm mark. Perhaps an adjustable 1.5K would be ideal ?? If you have
access to surplus suppliers or other ahem, "older" enthusiasts you may find
something there ??

--
Regards ............... Rheilly Phoull

 

[John Fields]

On Thu, 1 Jan 2004 23:34:52 -0000, "garry parker" <nospam@nospam.com>
wrote:

I need to build a power supply for a tube amp.
My transformer has an output of 240 volts, but after rectification this
rises to 330 volts.
I need a supply ouput of 250v dc.
Is there any way that I can reduce the 330 volts to 250 volts?
The transformer is rated at 100ma, and the amp will be drawing about 65ma.
The supply doesn't need to be regulated.

---
If your amp draws 65mA all the time then you could probably get away
with a resistor either in series with the primary or in the secondary
circuitry. If it doesn't draw 65mA all the time, then you _may_ need
some kind of regulation depending on the voltage excursions your amp can
take. What's your application like?

--
John Fields

 

[garry parker]

It's a class a amp so I understand it draws its full working current all the
time.
Garry

"John Fields" <jfields@austininstruments.com> wrote in message
news:309bvvsl4dqt00pa8gcvglghkpmp4lnlrr@4ax.com...

On Thu, 1 Jan 2004 23:34:52 -0000, "garry parker" <nospam@nospam.com
wrote:

I need to build a power supply for a tube amp.
My transformer has an output of 240 volts, but after rectification this
rises to 330 volts.
I need a supply ouput of 250v dc.
Is there any way that I can reduce the 330 volts to 250 volts?
The transformer is rated at 100ma, and the amp will be drawing about
65ma.
The supply doesn't need to be regulated.

---
If your amp draws 65mA all the time then you could probably get away
with a resistor either in series with the primary or in the secondary
circuitry. If it doesn't draw 65mA all the time, then you _may_ need
some kind of regulation depending on the voltage excursions your amp can
take. What's your application like?

--
John Fields